The "number of countries" is a misleading metric for landmine treaty - as it includes all the many countries who expect no wars at all and so they're not actually giving up anything. The 33 include almost all countries who actually expect to fight any wars and/or have serious militaries. Okay, UK, France and Turkey have banned landmines, but USA, Russia, China, India, Pakistan, Israel and Iran haven't banned them, and those 7 matter far more than the 164 signatories of the Ottawa convention for actual banning of landmines in practical use.
And of course, the roadside IEDs that USA saw in Iraq and Afghanistan would still be legal under the Ottawa convention (it does not ban anti-vehicle mines and remotely detonated devices) so you can't really assert that USA is complaining about something they won't ratify themselves.
If we look at the history of landmines, then it's fairly certain that countries are not going to give up a capability that they expect to use, all the universally accepted treaties only ban things that we consider impractical, which do not give a serious advantage (e.g. chemical weapons, which aren't competitive with conventional weapons if you're fighting against a proper military and not just gassing civilians and/or guerillas).
So combat robots will be banned only if (and while) they turn out to be useless and impractical compared to alternatives, or perhaps selectively banned by the countries who weren't going to use them anyway because they can't afford them. If they are actually good for their role, then they will be legal for all the major militaries.